<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <button onclick="getValue()">获取</button>
    <input type="text" name="username">

    <div></div>
    

    <script>

        function getValue(){
        var input = document.getElementsByName('username')[0];
        var div = document.getElementsByTagName("div")[0];
        var text = input.value;
        //标签不能在引号内需要拼接
        div.innerHTML = "<h1>"+text+"</h1>"

        }
        
    </script>
</body>
</html>